1. Field of the Invention
The present invention relates to an ink ribbon cassette for use in a thermal transfer printer in which the ink on an ink ribbon is melted and transferred by means of selective heating of heat producing elements of a thermal head thereof to perform desired printing, and also relates to a feed mechanism of such ink ribbon in a thermal transfer printer.
2. Description of the Prior Art
In a conventionally known thermal transfer printer, a recording medium such as a sheet of paper or the like and an ink ribbon having a desired ink applied on a base material which is formed of a resinous film are supported in front of a platen. A thermal head having a plurality of linearly arranged heat producing elements are mounted on a carriage. The ink ribbon is transported while reciprocating the thermal head together with the carriage along the platen. By selectively heating the heat producing elements of the thermal head on the basis of printing information, a desired printing is obtained on the recording medium.
FIG. 13 shows a widely used conventional thermal transfer printer. A frame 1 has a flat plate-like platen 2 attached thereto with its printing surface set substantially perpendicular thereto. A carriage shaft 3 traverses the frame 1 in parallel to the platen 2 at the lower front of the platen 2. Further, a flange-like guide portion 4 is formed at the front end edge of the frame 1, and a carriage 5 is attached to the carriage shaft 3 and the guide portion 4 in a manner capable of reciprocating along the carriage shaft 3 and the guide portion 4.
Also, a thermal head 6 is attached to the front end portion of the carriage 5 in a manner facing the platen 2 and capable of moving into and out of contact with the platen 2 by means of a driver mechanism (not shown) (for example a cam mechanism provided on the carriage), and a ribbon cassette (see FIG. 14) to be described later is detachably mounted on the upper surface of the carriage 5, having an ink ribbon accommodated therein and guiding the ink ribbon to the position between the thermal head 6 and the platen 2. Further, provided respectively on the upper surface of the carriage 5 are a take-up bobbin 7 and a feed bobbin 8 for engaging reels of the ribbon cassette to take up the ink ribbon and to feed the ink ribbon.
Further a paper inserting opening 9 for feeding a sheet of paper (not shown) to the front of the platen 2 is formed at the back of the platen 2, and a paper feed roller 10 for transporting the sheet of paper at a constant speed is disposed at the portion of the paper inserting opening 9. A pressing roller 11 to be pressed by the paper feed roller 10 is rotatably disposed under the paper feed roller 10, and a paper feed motor 13 for rotating the paper feed roller 10 through a group of toothed wheels 12 is provided on one side surface of the frame 1. By thus driving the paper feed motor 13 to drive and rotate the paper feed roller 10, a sheet of paper inserted from the paper inserting opening 9 is transported as it is clamped by the paper feed roller 10 and the pressing roller 11.
As has been described, in a conventional thermal transfer printer, a sheet of paper is inserted from the paper inserting opening 9 and the inserted paper is clamped between the paper feed roller 10 and the pressing roller 11. The paper feed roller 10 is rotated by driving the paper feed motor 13 to forward the sheet of paper in the direction perpendicular to traveling direction of the carriage 5. In the state where the thermal head 6 is pressed against the sheet of paper by a predetermined pressing force, the carriage 5 is caused to travel. At the same time, while taking up the ink ribbon of the ribbon cassette by rotating the take-up bobbin 7, the thermal head 6 is driven on the basis of a desired printing signal so as to selectively heat desired heat producing elements. Thereby a desired printing is performed on the sheet of paper by melting and transferring the ink on the ink ribbon.
A conventional ribbon cassette for use in such a thermal transfer printer will now be described by way of the drawings.
FIG. 14 is a top view showing the main portions of a conventional ribbon cassette in its printing state, i.e., in the state where the thermal head 6 is pressed against the platen 2; and FIG. 15 is a front view of a guide roller to be used in the ribbon cassette.
As shown in FIG. 14, a ribbon cassette body 22 has a pair of reels 23 rotatably supported thereon, disposed with a predetermined interval therebetween so as to engage the take-up bobbin 7 and the feed bobbin 8 of the thermal transfer printer as described and it also has five guide rollers 24A, 24B, 24C, 24D, 24E rotatably supported thereon in a manner facing the ribbon path thereof.
The pair of reels 23, 23 are each formed in a substantially cylindrical shape and the ink ribbon 25 is wound on the circumferential surface of the respective reels 23, 23 from their respective ends. When mounted on the carriage 5 of the above described thermal transfer printer, one of the pair of reels 23, 23 is engaged with the take-up bobbin 7 to serve as a take-up reel 23A for taking up the portion of the ink ribbon 25 which has been used for printing and the other is engaged with the feed bobbin 8 to serve as a feed reel 23B for feeding the ink ribbon 25. Further, on the respective inner peripheral surface of the reels 23A, 23B, a plurality of key grooves 26, 26 . . . are formed with intervals in the circumferential direction thereof, and they are engaged with the above described bobbins 7, 8 by means of these key grooves 26, 26 . . . . In printing state, thus, the ink ribbon 25 is drawn from the feed reel 23B by means of traveling of the carriage 5 and the take-up reel 23A is driven to be rotated to take up the ink ribbon 25 in synchronization with the traveling of the carriage 5 so as to cause the ink ribbon 25 to run in the direction indicated by an arrow in the figure.
Further, as shown in FIG. 15, each of the above described guides 24 has flanges 24b, 24c formed on the two ends in the axial direction of a cylindrical body 24a thereof. The ink ribbon 25 is disposed between these 24b, 24c to eliminate quivering in the up and down direction of the ink ribbon 25 when it is run and to achieve a stable running.
Here, the guide roller 24B located to abut against the ink surface side of the ink ribbon 25 immediately after printing is positioned so that it may provide a peeling force by which the ink ribbon 25 may be peeled from the sheet of paper after printing.
Formed at symmetrical positions on the case body 22 of the ribbon cassette 21 at the side facing the above described platen 2 and the sheet of paper, are two concave portions 29A, 29B into which the thermal head 6 attached to the carriage 5 may be inserted and disposed, the thermal head 6 being inserted into the concave portion 29A on the left side as shown in the figure. It should be noted that the concave portion 29B on the right side as shown in the figure is provided so that the ribbon cassette 21 may be used upside down when the ink ribbon 25 on one surface has been used to the end, in the case of accommodating an ink ribbon which may be used for a plurality of times. Further, fixed guides 30, 30 each having a curved surface in the direction facing the platen 2 are provided on the two sides of each of the concave portions 29A, 29B.
Here, while various types of paper may be used as the recording sheet in printing, a different type of ink ribbon is to be used in printing, for example, between a sheet of plain paper which is an ordinary recording sheet and an OHP sheet consisting of a light transmitting plastic sheet for use in an overhead projector.
Specifically, among those used as the ink ribbon 25A for use in printing of a sheet of plain paper are: one constructed as shown in FIG. 16(A) in which an ink layer 36 mixing a dye such as of carbon and a resin is laminated on the surface of a base 35 of a resinous film such as polyethylene terephthalate and an overcoat 37 of a high viscosity material such as polyamide is laminated on the surface of the ink layer 36; and one constructed as shown in FIG. 16(B) in which a heat-soluble peeling layer 38 of a wax is placed between a base 35 and an ink layer 36.
In performing printing on a sheet of plain paper using such ink ribbon 25, after driving the above described thermal head 6 to melt/transfer the ink layer 36 of the ink ribbon 25 onto the sheet, an excellent print is obtained by performing hot peeling in which the ink ribbon 25 is peeled away from the sheet of plain paper in the state where the transferred ink layer 36 of the ink ribbon 25 is still at a high temperature and is in its half-molten state and when cohesive force in the ink layer 36 is small. For this reason, it is constructed to make shorter to the extent possible the distance between the printing portion by the thermal head 6 and the peeling portion of the ink ribbon 25.
On the other hand, one example of the ink ribbon 25 for use in printing on the above described OHP sheet is constructed as shown in FIG. 16(C) such that an ink layer 39 of a mixture of a dye such as carbon and a wax is laminated on the surface of a base 35 of a resinous film.
In printing on the OHP sheet using such ink ribbon 25, after driving the above described thermal head 6 to melt/transfer the ink layer 39 of the ink ribbon 25 onto the OHP sheet, cold peeling is performed in which the ink ribbon 25 is peeled away from the OHP sheet after the molten portion of the ink layer 39 is cooled to be solidified. This is because it is necessary to make smooth the surface of the ink layer to prevent irregular reflection of light at the surface of the ink layer transferred to the OHP sheet. For this reason, it is required to make longer the distance between the printing portion by the thermal head 6 and the peeling portion of the ink ribbon 25.
Since, as described, the position at which the ink ribbon 25 is to be peeled away from the recording sheet is different between printing onto a sheet of plain paper and printing onto an OHP sheet, a thermal transfer printer capable of performing printing on both a sheet of plain paper and an OHP sheet has conventionally been constructed as shown in FIG. 17 to have a peeling roller 40 for varying the peeling position of the ink ribbon 25.
Specifically, disposed on the upper surface of the carriage 5 at the downstream side of the thermal head 6 in the direction of running of the ink ribbon 25, is a peeling lever 41 which is operated to be turned between the position of the solid line and the position of the broken line as shown in the figure by a drive mechanism,(not shown) of a solenoid or the like. Formed at the terminal end portion of the peeling lever 41 in a manner projecting upward therefrom, is a peeling roller 40 of which the surface to be moved into and out of contact with the ink ribbon 25 is covered for example with a sponge.
Here, the printing state onto the OHP sheet is defined by the case where the peeling lever 41 is operated to the position of the solid line as shown in the figure. The peeling roller 40 comes close to the platen 2 so as to be pressed by the ink ribbon 25. By delaying peeling of the ink ribbon 25 from the recording sheet, cold peeling is performed in which the ink ribbon 25 is peeled away from the recording sheet after the ink layer 39 of the ink ribbon 25 is cooled to be solidified. Further, the printing state onto a sheet of plain paper is defined by the case where the peeling lever 41 is operated to the position of the broken line as shown in the figure. By positioning the peeling roller 40 within the ribbon cassette 21 in a manner separated from the ink ribbon 25, the ink ribbon 25 is immediately stripped from the recording sheet as it is passed by the thermal head 6. Thereby hot peeling is performed in which the ink ribbon 25 is peeled away from the recording sheet while the ink layer 36 of the ink ribbon 25 is still in its molten state.
Further, in such thermal transfer printer, the shape of a cassette case is varied according to the type of the ink ribbon 25 and detection switch (not shown) disposed on the carriage is operated to be ON and OFF in accordance with the change in the shape to identify the type of the ink ribbon 25. Based on the detection result, then, for example, control is effected in the case of the ink ribbon for use in cold peeling so as to make longer the peeling distance of the ink ribbon by operating the peeling roller to perform cold peeling, or control is effected in the case of the ink ribbon for use in hot peeling so as not to operate the peeling roller to perform hot peeling with the peeling distance of the ink ribbon being relatively shorter as it is.
Furthermore, even in the ink ribbon for use in hot peeling, a number of types of ink ribbon are included, such as ink ribbons of monochrome or colored, a "one time" ribbon which may be used only once for printing or a "multi-time" ribbon which may be used in printing for a plurality of times, or a thin-type ink ribbon for accommodating a longer ink ribbon by thinning the thickness of the ink ribbon as a whole. It is necessary to provide suitable control according to each type, for example with respect to time of electrical conduction to the thermal head 6. Since it is required to discriminate each ink ribbon type from another, a large number of cassettes different in their shape are required to correspond to the respective ink ribbons if they are to be discriminated by shape. Thereby the number of the ribbon cassettes as component parts is increased, resulting in a problem that costs are increased.
Further, in the printing operation in hot peeling of the above described thermal transfer printer, not all the ink is transferred to the sheet by printing, and an ink layer 36a in its molten state remains as shown in FIG. 18 on the surface of the ink layer side of the ink ribbon 25 immediately after the printing, and this ink layer 36a possesses a tackiness. Thus, if feed amount of the ink ribbon after completing the printing equals to the traveling amount "A" of the carriage, the ink layer 36a in its molten state is stopped in the state where it abuts against the guide roller 24B, resulting in a problem that, when it is cooled as time elapses, the ink ribbon 25 and the guide roller 24B are stuck to each other. To prevent this, forwarding of the ink ribbon 25 until the ink ribbon 25 after printing completely passes the guide roller 24B ("B" in FIG. 19) may be considered. If so controlled, however, an extra amount of the ink ribbon 25 is to be forwarded, resulting in a problem that the wasteful consumption of the ink ribbon 25 is increased.
Further, in the conventional ribbon cassette as described, there has been a problem that, in the case of moving the carriage 5 in the "head-up" state where the thermal head 6 does not abut against the platen 2, for example when the sheet is transferred toward the side of the ink ribbon 25 at the time of line feed, the ink at the portion of the ink ribbon 25 supported by the fixed guides 30, 30 and the sheet abut against each other in a manner of rubbing, causing a tinting of the sheet where the ink adheres to the sheet as a stain.
Further, in the conventional thermal transfer printer as described, switching is made between hot peeling printing and cold peeling printing to control printing only by operating the peeling lever 41 to cause the peeling roller 40 to move toward and away from the platen 2. Not much problem is thus caused at the time of hot peeling printing. Since, however, in the case of performing cold peeling printing, the ink ribbon 25 is to be taken up by a winding force similar to that at the time of hot peeling printing, the peeling roller 40 may be moved away from the platen 2 due to the attaching play of the peeling lever 41 or due to the deformation of the sponge on the surface of the peeling roller 40. There has thus been a problem that a sufficient distance to the peeling of the ink ribbon which is required in cold peeling of ink ribbon cannot be secured where a suitable cold peeling printing cannot be performed. If taking up force of ink ribbon is set to a relatively weak level to solve this, a suitable cold peeling printing may be performed. In such a case, however, a problem occurs at the time of hot peeling printing that a suitable hot peeling printing cannot be performed because a sufficient peeling force of ink ribbon cannot be obtained or because timing for peeling is delayed.
Furthermore, in the above described thermal transfer printer, printing is performed while moving the carriage 5 in the state where the thermal head 6 is pressed against the sheet. The ink ribbon 25 is drawn from the side of the feed reel 23B with the traveling of the carriage 5 due to pressing of the thermal head 6 against the platen 2. At this time, however, problems occur such that the ink ribbon is moved diagonally where stable running cannot be obtained or that the ink ribbon 25 is consumed in a short time period, because the taking up amount of the ink ribbon 25 equals to the amount of traveling of the carriage 5.